The big picture: Fungi play a role in plant function

  • 100,000 species described
    • estimated 1.5 millions species
    • diverse size, morphology and habitats


  • Heterotrophic: eat via absorption
    • parasites, decomposers, mutualists
    • cycle nutrients via decomposition


  • Cell walls made of chitin
    • mushrooms are only a part of the body
    • filaments belowground absorb things


  • Wild reproduction

All Fungi share traits related to nutrition




  • Use enzymes to break down compounds
    • diverse enzymes for diverse food sources




  • Heterotrophs: absorb nutrients from environment
    • decomposers: break down dead things
    • parasites: absorb from host
    • mutualist: absorb/share with host

Fungal body plan: Not-motile

Most hyphae divided into cells by septa

Mycelium: huge surface and volume for absorption

Specialized hypae in many types of fungi


  • Specialized hyphae for feeding on live animals
    • hoops
  • Specialized hyphae that allow them to extract nutrients from plants

Mycorrhizal fungi: sharing with plants



  • ~80-90% of plants have association with fungus
    • fungi grown in/around plant roots
    • share resources
    • one of the most widespread mutualisms


  • 2 main types:
    • Ecto- and Endo- mycorrhizae
    • diverse array of species for each


  • Association now key for plants to thrive
    • fungi more efficient @ nutrient uptake




  • Branching hyphae used to exchange nutrients with plant hosts


  • Ectomycorrhizal fungi sheath cell walls
    • Hartig net surrounds epidermal cells


  • Endomycorrhizal fungi invade cell walls
    • Arbuscules: highly branched hypae inside cells
    • often called ‘arbuscular’ mycorrhizae

Nutrient Exchange: Sharing is caring




  • Inorganic nutrients imported to plant
    • N, P and amino acids


  • Carbon imported to fungus
    • sugars from photosynthesis


  • Possibly active & passive transport

Soil Life: Plant Roots, Fungi & Microbes


  • Free-living microbial communities in soils breakdown organic matter
    • plants cannot uptake organic compounds
    • fungi lost breakdown enzymes via evolution


  • Microbial communities are carbon limited
    • plants exude carbon (simple sugars) from root tips
    • exudates increases microbial activity


  • Fungi are great at uptake and transport
    • decomposers of some things
    • carbon limited

Timing matters: Land plant evolution & fungi


  • Fungal phyla associated with MS diverged prior to the divergence of land plants
    • Oldest fungal fossils appear ~900 mya
    • First terrestrial fungus ~ 460 mya


  • What was the land like for first plants?
  • What were early plants like?


  • Plant land colonization likely facilitated by interactions with symbiotic fungi
    • fossil evidence shows similarity in timing
    • needs of both groups still relevant

Early lineage plant experiments with fungi: byrophytes

Humphreys et al. 2010

Timing matters: Fossil forests and fungi


  • Vascular plants evolved secondary growth (wood), with lots of lignin
    • lignin is hard to break down


  • About 100 million years of trees sinking into swamps and not decaying
    • carboniferous period = coal deposits


  • Specialized phyla of fungi evolved as wood decay specialist
    • ~295 mya (aka ‘white rot’ fungus)
    • lignin and cellulose


  • What what the world look like today, without this key cog in the carbon cycle?

The current state of agriculture: Role of fungi


  • Dramatic ↑ in crop productivity last century
    • development of pesticides, fertilizers
    • plant breeding and genetic technologies


  • Now, crop yields have plateaued & fertilizer production unsustainable
    • climate change
    • over population
    • nutrient depletion
    • energy prices


  • High levels of fertilizer reduces fungal-root association


  • Big challenges to global food security

Role of mycorrhizae in agrosystems: Nutrients


  • Crop species are breed to be hyper-productive
    • fast growing with high yields


  • Roots will rapidly deplete soil nutrients
    • creates depletion zones around root


  • Mycorrhizae extend the reach of roots
    • widening the depletion zone


  • Mycorrhizae access nutrients in forms plants cannot
    • phosphorus from DNA or bound to minerals

Role of fungi in agrosystems: Stress, Disease


  • Pesticides hinder plant’s natural immune response
    • fungicides are toxic to mycorrhizal fungi


  • Fungi colonizing roots physically exclude and protect from pathogens
    • fungi release antibiotic substances


  • Communication through fungi allows neighboring plants to know of pest attacks


  • Mycorrhizal inoculation enhanced enzyme response to tomato blight infection
    • Song et al. 2015

Sustainable agricultre with mycorrhizae


  • Plant herbivory signals through fungal network between plants
    • neighbors can turn on chemical defenses
    • fungi help induce these chemical defenses (VOC’s)


  • Nutrients benefits of symbiosis mean more flowers & nectar
    • increases pollination


  • Fungal hypae release polysaccrides that bind soil particles
    • holds more water
    • stores more carbon
    • reduces erosion & leaching
    • improves microbial biodiversity

Should we also innoculate crops?


  • Commercial fertilizers (NPK) are water-soluble
    • short term availability
    • requires heavy fertilizer application


  • Natural abundances of soil nutrients exist, just not readily/easily accessible to plants


  • Tilling soil reduces natural mycorrhizal associations


  • Commercial inoculates add fungal spores, which are activated by root exudates

Are fungi always a good thing?


  • Fungal pathogens exist (non-mycorrhizal)


  • Not all crops have fungal symbioses
    • broccoli, mustard, spinach, beets
    • does this create competition?


  • Dependency on mycorrhizae varies greatly
    • wheat and corn varieties


  • How far does ‘sharing is caring’ go?
    • can the relationship become parasitic?